Although Q fever was first diagnosed nearly 80 years ago; an efficacious vaccine that provides long- term protection from C. burnetii infection and is safe for repeated booster administrations is still unavailable. We have determined that either CD4 or CD8 T cells alone (without B cells) are sufficient for protection from virulent phase I C. burnetii and that the CD8 T cell response is associated with less deleterious tissue damage. Others have shown that antibodies to phase I C. burnetii LPS may be efficacious as well, and should be considered in any new vaccine formulation. Phase I C. burnetii LPS is known to differently affect its receptor, TLR4, and the downstream immune responses to C. burnetii in mice and humans, diminishing the utility of mice as a model of Q fever in humans. To overcome this deficiency in mice, we will utilize an hTLR4/MD2 transgenic mouse model (expressing human TLR4/MD2), which we have recently shown is more susceptible than wildtype mice to low dose C. burnetii infection. This new mouse will allow us to better analyze the in vivo response to phase I C. burnetii LPS and its utility as a vaccine antigen. To develop a new vaccine for Q fever, we plan on using a novel delivery platform that uses P22 virus-like particles (P22 VLPs), which even in the absence of specific antigen induce adjuvant-like responses that nonspecifically protect mice from different viral and bacterial pathogens and minimize tissue morbidity associated with these pathogens. The P22 VLP can be uniquely engineered to express antigens on both the internal and external surfaces, which we have shown leads to selective enhancement of protective CD8 T cell and B cell responses, respectively. Specifically, our preliminary results suggest that P22 VLPs can be engineered to effectively induce antigen-specific non-damaging immune responses that could accommodate the requirements for a licensable C. burnetii vaccine. Thus, we hypothesize that VLPs can be engineered to generate an effective C. burnetii vaccine that induces only the protective and non-damaging adaptive immune responses (such as both CD8 T cell and antibody responses) locally in the lungs. Due to the non-damaging nature of the immune response elicited by the VLPs, we further hypothesize that this vaccine will be safe for repeatable administration. To test this hypothesis, we will pursue the following Specific Aims. Aim 1) Generate a VLP construct that induces CD8 T cell-mediated protection. This will be done by identification of C. burnetii immunodominant CD8 T cell epitopes that will be expressed on the internal surface of the P22 VLPs. Aim 2) Generate a VLP construct that induces anti-LPS antibody-mediated protection. The efficacy of VLP-delivered phase I C. burnetii LPS will be determined in humanized TLR4/MD2 mice immunized with VLP constructs expressing immunodominant CD8 T cell epitopes on the inside of the P22 VLPs and LPS on the outside of the same VLPs.